Central heating system design

14 Sep 2014
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United Kingdom
Can I get some feedback on this CHS design for an extended ground floor flat (75sqm total)?

Specifically, I'm thinking (1) the two radiators in the UFH kitchen/living area aren't needed and (2) to ditch the hallway radiator entirely.


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I really wish I knew, in the last 5 years all I thought I knew about central heating has been turned on it's head. The change came about well before that, but I had not realised. Some pointers.

1) The sun can really mess up your plans, mothers house the sun through the bay window could heat living room to 32°C before the TRV (thermostatic radiator valve) had time to react, had to change to electronic programmable type, that did improve it, so only 24°C when aim was 20°C, but points out sun can result in the needs for fast response, which means underfloor heating not suitable for those rooms.
2) Looking at the same room, I found the temperature through the room could vary by 5°C, windows being both cooler and warmer than centre of the room, which was an advantage as did not in the main sit in the window, so having radiators at 90° to window helped, I am sure done to reduce amount of pipework required, but having radiators in centre of home actually worked well, and really no point in heating outside wall.
3) Now I am going to reverse what I have said, the problem is we tend to put furniture around the walls, so we don't want to hide the radiator, so often we don't put furniture in the window, or at least if we do there is some circulation, air can enter under a couch, but often not under a book case. So there is a trade off.
4) Live style also changes requirements, in an old peoples care home you want heat 24/7 and nothing too hot to touch, so the under floor heating works well, but where the occupants go out to work, you have the reverse, what you are looking for is only to heat when required, so speed is required, the fastest wet central heating system is the fan assisted radiator, I had one in last house, did not really need geofencing as the Myson fan assisted radiator and a 4.5 kW gas fire in living room could heat the room in 15 minutes, however all Myson would really need piping in series with a modern boiler, for the boiler to modulate correctly, one odd one in kitchen fine, but all though house you can hear them running, and also rather expensive, so in the main not the best option for most, however being able to use same radiator to heat and cool is of course an advantage, but not a system I could afford.

I was rather disappointed with first attempt at geofencing, used electronic TRV heads, and the problem was the anti-hysteresis software was too good, so set to 20°C and sitting at 16°C it would heat to 18°C very rapid, but the last 2°C could take 3 hours, so I cheated, and set to 22°C for one hour then to 20°C to get around the anti-hysteresis software, this was great with a timed temperature change, not much use with a geofencing system. Oddly new house is reverse, the wall thermostat is not in the natural thermals so does not heat up fast enough, so hall where placed over shoots, so when we have been out, on return we have to turn down the hall temperature for an hour.

So I read the Drayton TRV heads use algorithms to counter this, and work out when to turn down so room heats fast and does not over shoot, but I have looked at price of the Drayton TRV heads, and like the Myson fan assisted radiators personally decided it was too expensive.

So I could continue, but by now your eyes are likely glazing over, and much will not apply to you. What I have realised is central heating is a compromise, there is no best system, and even things like leaving doors open or closed will affect how it works. My second house was a real problem as the heat went upstairs, being an open plan house, bedrooms could easy over heat.

So radiator position we can go through all the theory on natural thermals, but furniture can mean it will not work, my first house had the best system to ensure even room temperatures all controlled by one wall thermostat, it was gas hot air, and a large fan blows the air around the house into rooms with ducting out of rooms with vents in the door, but at that time it was before double glazing and moving air resulted in windows cooling the house a lot, so very expensive, so better is air did not circulate back then.

I have 9 electronic TRV heads so in theory if not using a room, I don't need to heat it, and to warm house for return, I can set the rooms to start heating in sequence so all heat into room going to be used first, however with a 24 kW boiler and 3 kW radiator you don't need rocket science to see this is of limited benefit, hind sight is good, should have fitted over sized radiators, but when installed we did not have electronic TRV heads so no one thought about that.

House I have just left is now my sons, had an old gas boiler, on/off, it would not modulate, now changed to new modulating boiler, with old boiler the pump circulated the water rapid, it did not matter if hot water returned, new boiler the return water temperature controls boiler output, so pump runs slower, and the input temperature to radiator may be the same at say 80°C, but the return temperature needs to be around 40°C so average radiator temperature is reduced to 60°C, so a radiator that was rated at 3 kW now rated at 2 kW also now has double glazing, and well sealed doors so does not need as much heat to maintain the room temperature, but maintaining temperature was never a problem, what is wanted is to reach the temperature fast, so if it takes longer to heat the room, need to start heating it earlier.

So back to life style, I am retired, I go out on average one day a week for long enough to be worth turning down the heating, I have geofencing but really don't need it, son with wife working odd shifts, kids at school, and he works shifts, he does need geofencing, or at least a programmable system easy to adjust.

So back to it is all a compromise, pobody is nerfect.
Who designed this, you or an installer?
1) If the UFH is adequate and works properly and cost-effectively then possibly- but get them piped up and fitted anyway, removing them cos you don't use them is much cheaper and easier than trying to fit them later when you discover how expensive and inflexible ufh can be
2) Leave it in. It'll create a warm buffer between living spaces and outside and importantly the hallway will usually be where the room stat is.

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